High-analysis ammonium polyphosphate fertilizer



1966 T. P. HIGNETT ETAL 3,228,752

HIGH-ANALYSIS AMMONIUM POLYPHOSPHATE FERTILIZER Original Filed Sept. 8. 1961 2 Sheets-Sheet 1 SUPERPHOSPHORIC ACID ANHYDROUS 14 awo P205 AMMONIA 75 -so-/. P 0 (PREFERRED) A 37.. E COOLING REACTOR MOLTEN REACTED MATERIAL i v I SOLIDIFICATION GRANULATION J17 IBL )IZ COOLING J cRusHER :5 FINES OVERSIZE SCREEN PRODUCT INVENTORS. BY W /f W 1966 T. P. HIGNETT ETAL 2 HIGH-ANALYSIS AMMONIUM POLYPHOSPHATE FERTILIZER Original Filed Sept. 8, 1961 2 Sheets-Sheet 2 TEMPERATURE, 4I5F TIME, 60 MINUTES om I e o I r; 2 D

,0 5.0 I 0 50 I00 I50 200 250 300 z PRESSURE, P 5. LG. '3 z- [-1 .5 9 5 Z O E 8.0 I I IL PRESSURE, 25 P s. I. G. 0 TIME, so MINUTES DJ M 7.0 g LIJ D TEMPERATURE, DEGREES F (7m z /Q W INVZITORs.

United States Patent 3,228,752 HIGH-ANALYSIS AMMONIUM POLYPHOSPHATE FERTILIZER Travis P. Hignett, Shetiield, and John G. Getsinger, Florence, Ala, assignors to Tennessee Valley Authority, a corporation of the United States Original application Sept. 8, 1961, Ser. No. 136,960, now Patent No. 3,171,733. Divided and this application Sept. 27, 1962, Ser. No. 227,664

9 Claims. (Cl. 23-107) (Granted under Title 35, U.S. Code (1952), see. 266) The invention herein described may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty therefor.

This application is a division of our copending application, Serial Number 136,960, filed September 8, 1961, now Patent No. 3,171,733, for High-Analysis Ammonium Polyphosphate Fertilizer.

Our invention relates to a new high-analysis solid fertilizer material suitable for preparing high-analysis liquid mixed fertilizers, and more particularly to a solid fertilizer material produced by reacting anhydrous ammonia and highly concentrated phosphoric acid.

Heretofore, liquid mixed fertilizers having compositions similar to those of standard dry mixed fertilizers have been well known, and such fertilizers are increasing in popularity in the industry. Such solutions have numerous advantages over dry mixed fertilizers in that the costs of evaporating moisture and bagging the product are eliminated. Such liquid fertilizers greatly simplify the operation of applying plant nutrients to the soil.

However, liquid fertilizers have in the past had some outstanding disadvantages. Raw-material costs have proved to be relatively high, and the solutions produced have been so corrosive as to result in high maintenance and storage costs. The liquid fertilizer solutions produced by the prior-art methods also have been limited to a maximum content of plant food of about 33 weight percent. This upper limit of available plant nutrients in prior-art solutions results from the fact that solutions having concentrations in excess of this amount always have been found to crystaliize and precipitate salts out of solution when stored at or below room temperature.

A recent breakthrough in the above-mentioned maximum content of plant-food units in liquid mixed fertilizers is shown in U.S. Letters Patent No. 2,950,961, Marcus M. Striplin, Jr., et. al., assigned to the assignee of the present invention. Striplin teaches the production of liquid mixed fertilizers which ordinarily contain as much as 60 weight percent plant food. Thus unusually high percent of plant food content is obtained in his process by ammoniating superphosphoric acid under controlled conditions. Superp-hosphoric acid, a concentrated phosphoric acid having generally from about 72 percent to about 85 percent P 0 content, is rapidly becoming a popular raw material in the fertilizer industry for the production of liquid fertilizers.

The term superphosphoric acid used in this specification and claims is defined as a phosphoric acid containing substantial quantities of both orthoand polyphosphoric acids. These polyphosphoric acids include pyrophosphoric acid and other polymers from the trito the nonapolymer and higher. The proportions of polyphosphoric acids vary with the P 0 content of the superphosphoric acid. The Canadian Journal of Chemistry, vol. 34 (1956),

3,228,752 Patented Jan. 11, 1966 page 790, shows that superphosphoric acid in the range from 69.81 to 84.95 percent P 0 contains the following proportions of orthophosphoric acid and polyphosphoric acids, expressed as percent of total phosphorus.

97.85 to 2.32 percent ortho- 2.15 to 49.30 percent pyro- 0.00 to 24.98 percent tri- 000 to 16.99 percent tetra- 0.00 to 12.64 percent penta- 0.00 to 9.75 percent hexa- 0.00 to 8.62 percent hepta- 0.00 to 7.85 percent octa- 0.00 to 6.03 percent nona- 0.00 to 29.41 percent higher polymers Alternatively, if wet-process phosphoric acid is concentrated from the usual maximum of about 54 percent P 0 up to the range of about to percent P 0 by a process such as shown in copending application of John G. Getsinger, Serial No. 835,377, filed August 21, 1959, and assigned to the assignee of the present invention, the distribution of 0rtho-, pyro-, and higher polymers of the polyphosphoric acids will be somewhat dissimilar to that shown in the abovementioned Canadian Journal of Chemistry. The presence of the impurities in such concentrated wet-process phosphoric acid, and the H O:P O ratio in acid so concentrated is believed to somewhat alter the distribution of the various polymers in this system.

Prior-art processes and methods for the production of concentrated fertilizers have proved to be operative; however, the industry has long felt the need for a high-analysis solid fertilizer material which may be processed without the undesirable step of evaporating moisture therefrom. In addition, the industry has desired a material which may either be directly applied to the soil or more preferably be readily soluble in water for effecting the production of relatively high-analysis liquid fertilizers just prior to application to the soil. The desirability of having a highanalysis solid material which is readily soluble in water for the production of liquid fertilizers is evidenced in the prior art in efforts to dissolve diammonium phosphate in aqueous media for the production of liquid fertilizers. Liquid fertilizers so produced are limited to a maximum grade of about 8-24-0, whereas we have found that by dissolving the product of our invention we obtain a liquid fertilizer of grade 11-33-0 and higher.

Our invention is directed to a new composition of matter which is readily soluble in water and extremely useful as a starting material for the production of high-analysis liquid fertilizers.

We have overcome the disadvantages inherent in both liquid mixed and dry granular fertilizers of the type shown in the prior art to a substantial extent in the present invention by providing a composition of matter which contains up to percent of its weight in the form of available plant food, and which is produced by a process of directly reacting anhydrous ammonia with concentrated phosphoric acid at elevated temperatures and pressures. Furthermore, several new, advantageous features over conventional dry mixed or liquid mixed fertilizer materials are realized by the present invention.

Among these advantages are convenience in the preparation of high-analysis liquid mixtures at or near the point of application to the soil and the sequestration of impurities in wet-process phosphoric acid. The composition of our invention has been found to have a sequestration properties equal to those of superphosphoric acid and the 1133() solution described in the above-mentioned Striplin et a1. patent. In addition, the composition of our invention has advantages over the liquid mixed fertilizers mentioned above in economy and convenience of transportation and storage. Transportation of liquid fertilizers has been handicapped by lack of transportation equipment. The expense of storing liquid fertilizers also has prevented many manufacturers from obtaining their supply before the peak season. During the peak season, there are not enough tank cars or trucks available to transport liquid material. In addition, there exists the possibility of crystallization of stored superphosphoric acid and liquid mixed fertilizers in extremely cold Weather.

The composition of our invention is free from these disadvantages, since it can be shipped in readily available boxcars and stored in open bins and it is unaffected by cold weather. Finally, the material of our invention is extremely water soluble.

As an illustration of the above-mentioned advantageous shipping economy of the material of our invention, it has been calculated that the freight on 1 ton of plant food in the form of an 11330 solution of the type mentioned in the Striplin et al. patent from Sheflield, Alabama, to Auburn, Washington, is about $65. However, the freight on 1 ton of plant food between the same two points in the form of the composition of our invention is only about It is therefore an object of the present invention to provide a new solid composition of matter and a process for its production, which composition contains unusually high amounts of available plant food.

Another object of the present invention is to provide a new solid composition of matter and a process for its production, which composition contains unusually high amounts of available plant foods and is readily soluble in water.

Still another object of the present invention is to provide a new solid composition of matter and a. process for its production, which composition contains unusually high amounts of available plant food, which is readily soluble in water, and which may be either directly applied to the soil in dry form or dissolved in an aqueous medium for preparation of high-analysis liquid fertilizers.

A further object of the present invention is to provide a new solid composition of matter and a process for its production, which composition contains unusually high amounts of available plant food, which is readily soluble in water, which may be either directly applied to the soil in dry form or dissolved in aqueous medium for preparation of high-analysis liquid fertilizers, and which is easily prepared from readily available raw materials.

In carrying out the objects of our invention in one form thereof we employ a reactor vessel, a stirring means, and other equipment. Our reactor vessel and associated equipment incorporate a pressure system which is operated at pressures and temperatures substantially above atmospheric. We have found it most economical to employ this type of equipment for both batchand continuous-mixing operations. Our invention, together with further objects and advantages thereof, will be better understood from a consideration of the following description, taken in connection with the accompanying drawings in which:

FIGURE 1 is a flowsheet illustrating principles of our process, which results in a solid fertilizer having the novel properties mentioned above.

FIGURE 2 is a graphical illustration showing the effect of reaction temperature on the degree of ammoniation of ammonium polyphosphate.

FIGURE 3 is a graphical illustration showing the effect of pressure on the degree of ammoniation of am monium polyphosphate.

Referring now more specifically to FIGURE 1, superphosphoric acid from a source not shown is fed through line 1 and any suitable means for controlling the rate of How 2 into a reaction zone comprising vessel 3. Anhydrous ammonia from a source not shown is fed into vessel 3 through line 4 and means 5 for controlling the rate of flow. Vessel 3 is equipped with a motor-driven agitator 6 running at such speed as to secure rapid and intimate mixing of acid and anhydrous ammonia to keep the resulting mixture in vigorous agitation until reaction is complete. Cooling coils 8 are located within vessel 3 and may be disposed in a baffle-like arrangement to increase the degree of agitation resulting from the action of agitator 6. We prefer to introduce a stream of superphospho-ric acid at a steady rate of flow according to the capacity of the equipment and to vary the rate of introduction of anhydrous ammonia as may be necessary to maintain the desired pressure of excess ammonia in the reactor.

The product is discharged from reactor vessel 3 through line 9 and any'suitable means for controlling the rate of flow 10 as a melt which solidifies upon subsequent cooling. The molten material from reactor vessel 3 is discharged into solidifier and granulator 11, where it is subjected to agitation by stirring means not shown. It has been found that agitation in vessel 11 is required to cause the molten material to set up into hard granules. The resulting hard granules are fed through line 12 into cooling means 13, which may comprise a rotary cooler or other conventional coo-ling equipment. The cooled, hard granular material travels from cooling means 13 via line 14 to a screening means generally illustrated as screens 15 and crusher 16. The crushed oversize material and the fine material are returned to granulator 11 via lines 17 and 18, respectively.

The acid fed to reactor vessel 3 may be either electricfurnace acid or concentrated wet-process acid. If electricfurnace acid is used, the concentration of P 0 should be about 74 to percent; however, products with superior physical properties are made when using acid con taining 75 to 80 percent P 0 Wet-process phosphoric acid can be used in this process in either batch-type or continuous-type operation. The desired concentration of the wet-process phosphoric acid will vary, depending upon the impurities present therein. When wet-process phoshporic acid is used, it is preferred that the acid contain about 65 to 75 percent P 0 The pressure maintained in reactor vessel 3 may be in the range from about 10 up to about 1000 pounds per square inch, depending upon other variables present in the process. However, the preferred operating pressure range has been determined to be about 10 to p.s.i.g. Increasing the pressure increases the degree of ammoniation, and the use of pressure in reactor 3 obviates any necessity for a scrubber or other means for controlling loss of ammonia.

In another embodiment of our invention, the use of pressure makes possible the use of automatic control of the feed rate of the ammonia to reactor 3. This is accomplished by using an automatic pressure-regulating valve in the ammonia feed line to control the pressure in the reactor. The flow of ammonia to reactor 3 will then automatically be equal to the amount that can be reacted under the conditions of operation.

The temperature in reactor 3 may be maintained in the range from about 325 F. to 475 F., with the preferred temperature range being about 350 F. to 385 F. Depending upon temperature and other variables, the retention time of the material in reactor vessel 3 may range from about 10 minutes to 3 hours, the preferred retention time being in the range of about 1 to 1.5 hours. We have found that increasing the retention time increases the degree of ammoniation of the product.

Motor-driven agitator 6 provides vigorous agitation in reactor vessel 3 and is required in order to effect intimate mixing of the anhydrous ammonia with the liquid ammonium polyphosphate in reactor 3. The intimate mixing so produced by agitator 6 has been found to increase the rate of reaction in vessel 3 and therefore the degree of ammoniation within a given retention time.

The hard, granular product of our invention is hereinafter referred to as ammonium polyphosphate. Microscopic and chemical examinations of products from various tests using 76 percent P phosphoric acid indicate that the product contains about 51 percent to 61 precent monoammonium orthophosphate, NH H PO about 38 percent to 46 percent tetraammonium pyrophosphate, (NI- F 0 and about 2 percent to 3 percent more highly condensed ammonium phosphates.

Several products made from 76 percent P 0 phosphoric acid are defined and described in Table I.

TABLE I about 325 F.). The cooling coil was made of As-inch stainless steel (A.I.S.I. Type 316) tubing. It provided 1 square foot of cooling area based on the external surface of the coil. The water was pumped through the cooling coil and discharged into a 1.5-gallon tank, from which it was recycled. This arrangement provided for utilizing the heat of reaction to heat the makeup water. The sup ply of cooling water in the tank remained at 212 F. Water was added to the supply tank as required to replace that evaporated.

Two electrical conductivity probes (electrodes), entering from the top of the reactor, were used to measure the level of the liquid in the reactor. The tips of the probes were /2 inch apart vertically. Each probe and the shell of the reactor formed a conductivity circuit. The liquid Description of ammonium polyphosphate product made from 76 percen1tP 0 phosphoric acid The reactor was constructed of stainless steel (A.I.S.I. Type 316) and was of l-gallon capacity. It was equipped with a turbine-type agitator and four bafiles /2 inch in Width by 11 inches high. Acid was fed from an overhead tank (-gallon capacity) with a reciprocating piston-type pump. The length of stroke of the piston could be varied to give the desired feed rate. The acid was fed at rates to give 10 to pounds of product per hour.

Gaseous ammonia was fed through a /2-inch line from pressure cylinders located outside the laboratory building. Warm Water was sprayed on the cylinders to obtain pressures of up to about 325 p.s.i.g. as required. The ammonia was fed into the reactor through a '%-inch tube. The tube was closed at the end, and a one-hole sparger was made by drilling a 0.052-inch hole at the end of the tube. The sparger Was located near the bottom of the reactor under the tip of the agitator. The reactor was equipped with a pressure gage, and the rate of feed of ammonia to the reactor was controlled manually with a throttling valve to give the desired pressure of excess ammonia in the reactor. The temperature was measured with a thermocouple and a recording potentiometer.

Since the reaction of ammonia and superphosphoric acid was highly exorthermic, it was necessary to provide cooling. Hot water Was used for cooling to prevent freezing of material on the cooling coil (freezing point of in the reactor completed the circuit when it touched a probe and caused a light bulb to burn. The reactor was operated to keep the level between the two probes, which was indicated by the top light being 05 and the other on. The level was controlled by the rate of drawoff of liquid from the bottom of the reactor by use of a Ai-inch throttling valve.

In the initial tests it was found that the degree of agitation in the reactor had a significant effect on the degree of ammoniation. The reactor first was equipped with a six-blade agitator impeller that was 2 /2 inches in diameter with blades /2 inch in width located one agitator diameter above the bottom of the reactor. The agitator was rotated at 600 r.p.m., and the degree of ammoniation was only about 5 pounds of ammonia per unit of P 0 Increasing the width of the agitator blades to 2 inches increased the degree of ammoniation to 6.3 pounds of ammonia per unit of P 0 when the speed of the agitator was 600 r.p.m. A further increase in degree of ammoniation to 7.5 pounds of ammonia per unit of P 0 resulted when the speed of the agitator was increased to 1730 r.p.m. No further increase was obtained when the speed of the agitator was increased to 2130 r.p.m. Effects of operating variables on the degree of ammoniation in tests of the production of ammonium polyphosphates are given in Table II.

TABLE 11 Efiects of operating variables on degree of ammoniation EFFECT OF AGITAIION Speed of Retention Product composition agitator, Temperature, Pressure, time Lb. Nils/unit r.p.m. F. p.s.i.g. minutes P EFFECT OF PRESSURE EFFECT OF TEMPERATURE EFFECT OF RETENTION TIME 1 Agitator was 2.5 inches in diameter and 2 inches wide except as noted in footnote 2.

2 Agitator, 2.6 inches in diameter and inch wide.

Temperature and pressure were related in their eflects on the degree of ammoniation and on the freezing point of the melt in the reactor. At pressures of 300 p.s.i.g., it was necessary to keep the temperature at 415 P. so that the melt would be fluid; at pressures of 25 p.s.i.g., temperatures as low as 365 F. could be used. The tests were made with an agitator speed of 2130 r.p.m. and a retention time of about 60 minutes. The results are shown in Table II and FIGURES 2 and 3.

The effect of pressure was measured at a reaction temperature of 415 F. Increasing the pressure from 25 to 300 p.s.i.g. increased the degree of ammoniation from 5.7 to 7.5 pounds of ammonia per unit of P 0 Tests of the eflect of temperature were made at a pressure of 25 p.s.i.g. Increasing the temperature from 365 F. to 450 F. decreased the degree of ammoniation from 7.0 to 5.3 pounds of ammonia per unit of P 0 At a reactor pressure of 25 p.s.i.g. and temperatures of 350 F. to 370 F., as the retention time was increased from 30 to 90 minutes, the degree of ammoniation increased from 6.8 to 7.2 pounds of ammonia per unit Of P205.

It is apparent that there are several combinations of pressure, temperature, and retention time which may be used to obtain a given degree of ammoniation. To obtain the highest degree of ammoniation high pressure, low temperature, and long retention time should be used; however, the physical limitation of. retaining a fluid melt that can be agitated must be met in setting the conditions of operation.

In order that thoseskilled in the art may better understand how the present invention can be practiced, the following examples are given by way of illustration and not by way of limitation.

EXAMPLE I Superphosphoric acid (76% P 0 was fed to the reactor at the rate of 2.6 pounds per hour. The flow of ammonia was regulated to give a pressure of 300 p.s.i.g. in the reactor. This resulted in a flow rate of 0.7 pound of ammonia per hour. The volume of the liquid retained in the reactor was 0.7 gallon. The retention time of the liquid in the reactor was 168 minutes. The temperature in the reactor (380 F.) was controlled by regulating the flow of water through the cooling coil. The agitator (2 A in., six-blade impeller) was rotated at 1000 r.p.m. Liquid product was discharged from the reactor at the rate of 3.3 pounds per hour. After collecting 9 pounds of liquid product, it was agitated with a propeller-type stirrer for 15 minutes until it solidified. The solid material was crushed and sampled for analysis. The analysis showed a nitrogen content of 17.9 percent and a P 0 content of 60.8 percent. The product was hard. It remained dry and free flowing even after exposure to a humid atmosphere.

EXAMPLE II In a run made in a reactor device similar to that de scribed in Example I, the following results were obtained.

Test No. 1

Superphosphoric acid concentration, percent P 0 75.9 Feed rate, lb./hr.:

Superphosphoric acid -1 25.0 Anhydrous ammonia 6.1 Reactor:

Agitator speed, r.p.m. 1000 Temperature, F. 420 Pressure, p.s.i.g 300 Retention time, minutes 18 Discharge rate, lb./hr 31.1 Product grade 15.961.0-0

The analysis of the above product indicates a fertilizer material of about 16-61-0 grade, and the material produced in this run remained dry and free flowing even after exposure to a humid atmosphere.

9, EXAMPLE III The results of another run made in a reactor device similar to that described in Example I are given below.

Test No 2 Superphosphoric acid concentration, percent P 76.1 Feed rate, lb./hr.:

Superphosph-oric acid 3.8 Anhydrous ammonia 0:9 Reactor:

Agitator speed, r.p.m. 1000 Temperature, F. 340 Pressure, p.s.i.g Retention time, minutes 118 Discharge rate, lb./hr 4.7 Product grade 16.662.50

The analysis of the above product indicates a fertilizer material of about 1763-0 grade, and the material produced in this run remained dry and free flowing even after exposure to a humid atmosphere.

EXAMPLE IV In still another run made in a reactor similar to that described in Example I, the following results were obtained.

Test N o 3 Superphosphoric acid concentration, percent P 0 75.7 Feed rate, lb./hr.:

Superphosphoric acid 27.4 Anhydrous ammonia 6.3 Reactor:

Agitator speed, r.p.m. 1000 Temperature, F. 350 Pressure, p.s.i.g 240 Retention time, minutes 16 Discharge rate, lb./hr. 33.7 Product grade 15.4-61.5-0

The analysis of the material made in this run indicated a fertilizer material of grade of about 62(), and the material so produced remained dry and free flowing even after exposure to a humid atmosphere.

EXAMPLE V The following results were obtained in another run made in a reactor device similar to that described in EX- ample I.

Test No 4 Superphosphoric acid concentration, percent P 0 76.4 Feed rate, lb./hr.:

Superph-osphoric acid 4.9 Anhydrous ammonia 1.4 Reactor:

Agitator speed, r.p.m. 2160 Temperature, F. 370 Pressure, p.s.i.g Retention time, minutes 9() Discharge rate, lb./-hr. 6.3 Product grade 17.8-59.7-0

The analysis of the material made in this run indicated a fertilizer material of a grade of about 1860-0, and the material so produced remained dry and free flowing even after exposure to a humid atmosphere.

EXAMPLE VI The results of yet another run are given below. The reactor in which this run was made was a device similar to that described in Example I.

Test No. 5

Superphosphoric acid concentration, percent P 0 76.3 Feed rate, lb./hr.:

Superphosphoric acid 6.9

Anhydrous ammonia 1.9 Reactor:

Agitator speed, r.p.m. 2130 10 Temperature, F 365 Pressure, p.s.i.g 25 Retention time, minutes 60 Discharge rate, lb./hr. 8.8 Product grade 17.3-59.8-0

The product material analyzed about 17-60-0, and it remained dry and free flowing even after exposure to a humid atmosphere.

EXAMPLE VII The following results were obtained in yet another run made in a reactor device similar to that described in Example I.

Test No. o

Granulation conditions were as follows: The molten slurry as sprayed through a nozzle directly onto a bed of recycled fines in a laboratory-size pugmill. Recycled fines (-12 mesh, Tyler) were fed to the pugmill by a disk feeder. The recycle rate was pounds per hour or 3.3 pounds per pound of product. The temperature of the material discharged from the pugmill was F. The screen analysis (Tyler) of the material from the pugmill was as follows:

PERCENT The product was hard, dry, and free fiowing even after exposure to a humid atmosphere.

EXAMPLE VIII Wet-process phosphoric acid which had been highly concentrated (711.4% P 0 was reacted batchwise with gaseous ammonia in a pressure-type reactor equipped with a propeller-type agitator. The procedure used is given below.

The acid (200 g.) was added to the reactor, and the reactor was closed. The reactor was then heated to 200 F. Gaseous ammonia (45 g.) was added at an average rate of 1.3 grams per minute for 35 minutes. At this time the reactor temperature had risen to a maximum of 325 F, and the pressure was 65 pounds p.s.i.g. Feeding of ammonia and agitation were discontinued at this time, the pressure was released, and the fluid mixture was poured out of the reactor. A longer period of reaction and agitation would have resulted in solidification of the material in the reactor. The fluid material from the reactor was agitated by hand stirring until the material became hard. Analysis of the product gave a nitrogen content of 15.2 percent and a P 0 content of 58.4 percent. The material was hard and free flowing.

While we have shown and described particular embodiments of our invention, modifications and variations thereof will occur to those skilled in the art. We wish it to be understood, therefore, that the appended claims are intended to cover such modifications and variations which are Within the true scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 325 F. to about 475 F. and under a constant pressure in the range from about 10 p.s.i.g. to about 1000 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; and withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

2. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 350 F. to about 385 F. and under a constant pressure in the range from about p.s.i.g. to about 100 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by Weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; and withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

3. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature of about 370 F., and under a constant pressure of about 25 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the infiowing superphosphoric acid; and withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

4. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 325 F. to about 475 F. and under a constant pressure in the range from about 10 p.s.i.g. to about 1000 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; retaining the material comprising said mass in said reaction vessel from about 10 minutes to about 180 minutes; and withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

5. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about percent available plant nutrients (NJ-P 0 from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 350 F. to about 385 F. and under a constant pressure in the range from about 10 p.s.i.g. to about 100 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia-and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; retaining the material com prising said mass in said reaction vessel from about 60 minutes to about minutes; and withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

6. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N-l-P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature of about 370 F., and under a constant pressure of about 25 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; retaining the material comprising said mass in said reaction vessel for about 90 minutes; withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate as product.

7. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 325 F. to about 475 F. and under a constant pressure in the range from about 10 p.s.i.g. to about 1000 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the infiowing superphosphoric acid; retaining the material comprising said mass in said reaction vessel from about 10 minutes to about 180 minutes; withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate; introducing said withdrawn molten material into solidification means; continuously agitating the solidified material in said solidification means, thereby causing the formation of hard granules in the resulting solidified material; cooling the resulting solidified and granular material; introducing said cooled material into sizing means; returning particles of predetermined size from said sizing means to said solidification means; and withdrawing from said sizing means hard granular ammonium polyphosphate material of predetermined size as product.

8. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (PH-P from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature in the range from about 350 F. to about 385 F and under a constant pressure in the range from about p.s.i.g. to about 100 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about 85 percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; retaining the material comprising said mass in said reaction bessel from about 60 minutes to about 90 minutes; withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate; introducing said withdrawn molten material into solidification means; continuously agitating the solidified material in said solidification means, thereby causing the formation of hard granules in the resulting solidified material; cooling the resulting solidified and granular material; introducing said cooled material into sizing means; returning particles of predetermined size from said sizing means to said solidification means; and withdrawing from said sizing means hard granular ammonium polyphosphate material of predetermined size as product.

9. A process for producing a solid, high-analysis ammonium polyphosphate fertilizer material containing about 80 percent available plant nutrients (N+P O from anhydrous ammonia and superphosphoric acid, which comprises maintaining in a closed reaction vessel at a temperature of about 370 F. and under a constant pressure of about 25 p.s.i.g., a mass of molten material of low viscosity, previously formed by combining anhydrous ammonia and superphosphoric acid therein, said superphosphoric acid containing in the range from about 74 percent P 0 to about percent P 0 by weight; continuously combining relatively small streams of said anhydrous ammonia and said superphosphoric acid into said mass of molten material; continuously vigorously agitating said mass of molten material, thereby keeping substantially the entire mass thereof well agitated and causing immediate ammoniation of the inflowing superphosphoric acid; retaining the material comprising said mass in said reacton vessel for about minutes; withdrawing from the bottom of said mass of molten material molten ammonium polyphosphate; introducing said withdrawn molten material into solidification means; continuously agitating the solidified material in said solidificaton means, thereby causng the formation of hard granules in the resulting solidified material; cooling the resulting solidified and granular material; introducing said cooled material into sizing means; returning particles of predetermined size from said sizing means to said solidification means; and withdrawing from said sizing means hard granular ammonium polyphosphate material of predetermined size as product.

References Cited by the Examiner UNITED STATES PATENTS 1,984,968 12/1934 Fiske et al 23-107 2,689,780 9/1954 Rice 23-107 X 2,902,342 9/1959 Kerley 23-107 3,044,851 7/1962 Young 23-107 3,053,622 9/1962 Bostwick 23-107 3,057,711 10/1962 Reusser 23-107 X BENJAMIN HENKIN, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

O. CRUTCHFIELD, Assistant Examiner. 

1. A PROCESS FOR PRODUCING A SOLID, HIGH-ANALYSIS AMMONIUM POLYPHOSPHATE FERTILIZER MATERIAL CONTAINING ABOUT 80 PERCENT AVAILABLE PLANT NUTRIENTS (N+P2O5) FROM ANHYDROUS AMMONIA AND SUPERPHOSPHORIC ACID, WHICH COMPRISES MAINTAINING IN A CLOSED REACTION VESSEL AT A TEMPERATURE IN THE RANGE FROM ABOUT 325*F. TO ABOUT 475*F. AND UNDER A CONSTANT PRESSURE IN THE RANGE FROM ABOUT 10 P.S.I.G. TO ABOUT 1000 P.S.I.G., A MASS OF MOLTEN MATERIAL OF LOW VISCOSITY, PREVIOUSLY FORMED BY COMBINING ANHYDROUS AMMONIA AND SUPERPHOSPHORIC ACID THEREIN, SAID SUPERPHOSPHORIC ACID CONTAINING IN THE RANGE FROM ABOUT 74 PERCENT P2O5 TO ABOUT 85 PERCENT P2O5 BY WEIGHT; CONTINUOUSLY COMBINING RELATIVELY SMALL STREAMS OF SAID ANHYDROUS AMMONIA AND SAID SUPERPHOSPHORIC ACID INTO SAID MASS OF MOLTEN MATERIAL; CONTINUOUSLY VIGOROUSLY AGITATING SAID MASS OF MOLTEN MATERIAL, THEREBY KEEPING SUBSTANTIALLY THE ENTIRE MASS THEREOF WELL AGIATED AND CAUSING IMMEDIATE AMMONIATION OF THE INFLOWING SUPERPHOSPHORIC ACID; AND WITHDRAWING FROM THE BOTTOM OF SAID MASS OF MOLTEN MATERIAL MOLTEN AMMONIUM POLYPHOSPHATE AS PRODUCT. 